Mammalian IL-7 had been previously designated "Lymphopoietin-1." The cloning and expression of human and murine IL-7 has been described in U.S. Pat. No. 4,965,195, issued on Oct. 23, 1990, the disclosure of which is incorporated by reference herein. IL-7 is a lymphopoietic growth factor that was first isolated and cloned by virtue of its ability to stimulate the growth of B- and T-cell progenitors in bone marrow. Published PCT Application WO 89/03884 (May 5, 1989) and EP-A-0314415 (May 3, 1989) disclose DNAs, vectors and related processes for producing IL-7 by recombinant DNA technology. The relevant disclosures of these published patent applications are incorporated by reference herein. The cloning of murine IL-7 was first reported in the scientific literature by Namen et al., Nature 333:571 (1988) and human IL-7 by Goodwin et al., Proc. Natl. Acad. Sci. USA 86:302 (1989). Purification of murine IL-7 from supernatants of transformed bone marrow stromal cells lines indicated an apparent molecular weight of approximately 25,000 daltons (see, e.g., Namen et al., J. Exp. Med. 16:7988 (1988)). The cDNA sequences reported by Namen et al. and Goodwin et al. suggest minimum molecular weights for murine and human IL-7 polypeptides of 14,897 and 17,387 daltons, respectively, exclusive of any glycosylation. Cloning, characterization and expression of IL-7 has enabled the characterization of its spectrum of biological activities.
IL-7 was originally defined by its ability to stimulate proliferation of pre-B cells (B220.sup.+) derived from long-term bone marrow culture (Whitlock et al., J. Immunol. Methods 67:353-69 (1984)). IL-7 was unable, however, to stimulate proliferation of mature B cells or to induce differentiation of pre-B cells to surface Ig.sup.+ cells (Lee et al., J. Immunol. 142:3875-83 (1989)).
Previous investigations with IL-7 suggested that only T lineage cells respond to this cytokine. For example, resting fetal and adult thymocytes of most surface phenotypes proliferate in response to IL-7 in a manner independent of Interleukin-2 (IL-2), Interleukin-4 (IL-4), or IL-6 (Conlon et al., Blood 74:1368-73 (1989) and other references). Further, mature peripheral T cells respond to IL-7 in the presence of suboptimal mitogen concentrations (Chazen et al., Proc. Natl. Acad. Sci. USA 86:5923-27 (1989)). Morrissey et al., J. Exp. Med. 169:707-16 (1989) have shown that IL-7 can provide a co-stimulatory signal for the in vitro proliferative response of purified murine T cells to Con A by inducing IL-2 production. Additionally, Chazen et al., supra, have further shown that IL-7 in combination with PMA can directly stimulate T cell activation without intervention with another cytokine messenger. Response to a combination of IL-7 and PMA was not inhibited by high concentrations of neutralizing antibodies to either IL-2 or IL-4 and was largely resistant to immunosuppressive effects of CsA, a drug which inhibits the transcription of a number of lymphokine genes, including those encoding IL-2, IL-4 and Interferon-.gamma..
Many recent investigations utilizing IL-7 have focused upon T cell-mediated activity conferred by this cytokine. For example, Alderson et al., J. Exp. Med. 172:577-87 (1990) have shown that purified recombinant IL-7 can generate cytolytic T lymphocytes (CTL) in mixed lymphocyte culture. IL-7 was further shown to induce lymphokine-activated killer cells in autologous cultures of human peripheral blood mononuclear cells. The authors postulated that much of the IL-7 activity to induce CTL was accomplished via IL-2 production.
Park et al., J. Exp. Med. 171:1073-89 (1990) report that receptors for IL-7 have been demonstrated on lymphoid cells and myeloid lineage cells. However, no activity for IL-7 on monocytes/macrophages or neutrophils has been reported.
Other cytokines have been reported to stimulate macrophages or monocytes to produce a cytokine response. For example, Donnelly et al., J. Immunol. 145:569-75 (1990) report that the endotoxin LPS (lipopolysaccharide) stimulated monocyte production of IL-1.beta., TNF-.alpha., and IL-6 and that cytokine production stimulated by endotoxin was inhibited by exposure of the macrophages to IL-4. Moreover, IL-4 was reported to suppress IL-1 production induced by a variety of monocyte activation stimuli, including LPS, PMA, and Staphylococcus aureus. Donnelly et al. further report that Interferon-.gamma. (IFN-.gamma.) enhanced monocyte IL-1 production induced by LPS. IL-4 largely neutralized the potentiating effects of IFN-.gamma.. Therefore, cytokines IFN-.gamma. and IL-4 can influence the state of monocyte activation by either up-regulating (IFN-.gamma.) or down-regulating (IL-4) the expression of IL-1.
IL-1 can further induce IL-6 production in peripheral blood monocytes. For example, Tosato et al., Blood 75:1305-10 (1990) reported that IL-6 production can be induced in monocytes by the endotoxin LPS, IL-1, TNF-.alpha. and Platelet-Derived Growth Factor (PDGF).
It appears that one of the primary functions of peripheral blood monocytes is to regulate synthesis and secretion of an array of biologically active molecules, including enzymes, plasma proteins and cytokines. Monocyte-derived cytokines include IL-1.alpha., IL-1.beta., IL-6, IL-8, and TNF-.alpha.. All of these cytokines, produced by monocytes, have broad immunoregulatory properties that are central to the host response to infection. Microbial products, such as LPS and peptidoglycan, are effective inducers of cytokine secretion by monocytes. More recently, monocyte-synthesized cytokines have been demonstrated to regulate monocyte cytokine synthesis. In particular, IL-1.alpha., IL-1.beta., TNF-.alpha., TGF-.beta., (Transforming Growth Factor-.beta.) IFN-.gamma., GM-CSF and IL-3 have all been shown to stimulate some aspect of monocyte cytokine secretion, either acting alone or in combination with other stimuli. Conversely, IL-4 has potent antagonistic effects on the induction of monocyte activation, including both cytokine secretion and respiratory burst activity.
Accordingly, there is a need in the art to determine if IL-7 can affect monocyte function and whether IL-7 can be used to stimulate the antimicrobial, tumoricidal and cytokine-releasing activities of macrophages.